Although it has been known for decades that opiates inhibit the reproductive cycle of the mammal via direct actions on the hypothalamus, little research has been done on the cellular mechanism of their action. The present proposal will evaluate firstly the physiological effects of the endogenous opioids on hypothalamic neurons, and secondly, the effects of chronic morphine on these same cells. Hypothalamic slices will be prepared from cycling female guinea pigs, and single electrode voltage clamp experiments will be done in order to elucidate the acute and chronic effects of opioids on the membrane properties of arcuate and cell-poor zone (ARC-CPZ) neurons. Dose response curves will be generated based on the changes in membrane current caused by specific opioid agonists. Schild analysis will be utilized to characterize the specific receptor(s) involved in the direct actions of the opioids, and the specific K+ and/or Ca+2 conductance(s) coupled to the receptor(s) will be ascertained. LHRH release from hypothalamic slices will be measured and Schild analysis of the inhibition of peptide release by specific agonists will be correlated with the voltage clamp data on single ARC-CPZ neurons. The effects of 17beta-estradiol (E2) on the acute actions of the opioids will be ascertained by using slices prepared from ovariectomized females and ovariectomized females that have received E2 replacement. Dose response curves will be established for specific opioid agonists mesuring ion conductances. LHRH release will also be measured in these same slices and shifts in the dose response curve and any changes in receptor affinity ascertained. Once the physiological role of the endogenous opioids in regulating the activity of ARC-CPZ neurons has been assessed, then studies will be initiated to determine the effects of chronic morphine on the electrophysiological properties of these cells and on the release of LHRH. Slices will be prepared from physically dependent and tolerant guinea pigs, and the changes in the opioid dose response and in their coupling to specific membrane conductances determined in ARC-CPZ neurons. It is envisioned that these studies will elucidate the physiological role of the opioids in the control of the mammalian reproductive cycle and the basis for the inhibition of the cycle with chronic abuse.